Description of experiment
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Needed compounds:
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sodium sulfite : Na2SO3
acetyl chloride : CH3COCl
anhydrous chromic acid : CrO3
Class:
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elem=S,Cr
redox
Summary:
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Sodium sulfite is not capable of reducing CrO3, dissolved in acetyl chloride.
As soon as water is added, the red color of the hexavalent chromium disappears
and green/blue trivalent chromium is formed.
Description:
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Add some solid chromium(VI) oxide, CrO3, to acetyl chloride: The CrO3 dissolves
and gives a beautiful deep red solution.
Add some solid sodium sulfite anhydrous, Na2SO3, to acetyl chloride: The solid
does not dissolve, or it dissolves only sparingly.
Add the red solution to the acetyl chloride with the sodium sulfite in it: The
liquids mix and a deep red solution is obtained, with solid Na2SO3 at the
bottom. At gentle heating, the liquid remains red. After several minutes and
continued shaking, the liquid still is red.
Dump the liquid at once in a beaker with some water in it: Big red drops of
liquid collect at the bottom. These drops quickly dissolve in the water,
sometimes producing bubbles of gas, which quickly dissolve again a few cm above
the drop on which they are formed. After a few tens of seconds, all drops have
dissolved and the resulting liquid is green. On shaking, it becomes bluish
green.